Radio noise suppressor

[watsondenmark]

Hi,

I have a 911 2,2T from 1971, former US car, but living in Europe now.
On the "electrics plate" in the engine compartment there is a radio noise suppressor.

Someone (former owner) cut the wire at the radio noise suppressor.

I used the internet to find out that it is a radio noise suppressor... But what do it do??? and where do I connect the wire???

In the picture it looks like it should be connected to the plate, but I can't see it in the wiring diagram.
It's number 7 at this picture (from a 1970). I only have the one in the top, and it doesn't look like the lower one ever has been there.

[4boer]

I am interested to see what people say. Do you have any radio problems? I have engine noise coming through the radio and this may be a cause. Here is a link that I found informative: Noise Suppression Guide - Noise Suppression Guide

[watsondenmark]

I don't have a radio in the car. I like the song of the flat six ;-)

Ist it really for the radio? I thaught it was there to prevent some kind of interferance in the CDI and alternator.

[Targalid]

It suppresses radio noise from the ignition system. I disconnected mine because it was wired between the alternator and the voltage regulator. I noticed that radio noise increased and matched engine speed. If you don't have a radio, don't worry about it.

[wwest]

Originally Posted by Targalid

It suppresses radio noise from the ignition system. I disconnected mine because it was wired between the alternator and the voltage regulator. I noticed that radio noise increased and matched engine speed. If you don't have a radio, don't worry about it.

Not that it really matters but it actually suppresses the RFI/EMI emanating from the voltage regulator PWM on/off current switching to/for the alternator rotor windings.

[Targalid]

Wwest,
Thanks for your knowledge. Maybe you can explain this wikipedia entry to us.

"Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a modulation technique that conforms the width of the pulse, formally the pulse duration, based on modulator signal information. Although this modulation technique can be used to encode information for transmission, its main use is to allow the control of the power supplied to electrical devices, especially to inertial loads such as motors. In addition, PWM is one of the two principal algorithms used in photovoltaic solar battery chargers,[1] the other being MPPT.
The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the load is.
The PWM switching frequency has to be much faster than what would affect the load, which is to say the device that uses the power. Typically switchings have to be done several times a minute in an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies."

So the voltage regulator supplies an exciter voltage to the alternator which is pulsed? This pulsed signal is radio frequency which is picked up by the car radio receiver? Is that the take home message? I'm a chemist not a EE so for me this is like Greek to that guy in Shakespeare.

[HawgRyder]

The object is a feed-through capacitor.
This means...it has a wire running through it....with the wire capacitively linked to the outside casing.
Depending on the value ...the frequency shunted to ground varies.
Also...the guage of the wire running through it determines the current carrying capacity.
So...they come in many sizes...with current and frequency being the value factors.
If you replace one...try to see the original specs to get the right one.
You can always go bigger on the current (size permitting) but the frequency is more important.
Bob

[watsondenmark]

Interesting reading.

Because I want to have my car as original as possible, I want to connect it.

The curly red wire looks like it's connected to the base of the Voltage regulator on the picture (mine is a S.E.V Marshal).

On my radio noise suppressor, it looks like it has a base to connect another wire.

What do I connect? And where?

[guru944]

watsondenmark;

Capacitor should be at Ignition (+) regulator or Coil or alternator output lead and Ground Chassis or engine. 3mf (25 vdc) is recommended or higher better.

F(t)=1/RC That is the Time Constant or Frequency
Most good Radio Noise Filters incorporate a RLC or LC passive filter circuit.

Visit this site it has very good tips: Identifying and suppressing radio interference | How a Car Works

later...

[wwest]

Originally Posted by guru944

watsondenmark;

Capacitor should be at Ignition (+) regulator or Coil or alternator output lead and Ground Chassis or engine. 3mf (25 vdc) is recommended or higher better.

F(t)=1/RC That is the Time Constant or Frequency
Most good Radio Noise Filters incorporate a RLC or LC passive filter circuit.

Visit this site it has very good tips: Identifying and suppressing radio interference | How a Car Works

later...

"...(+) regulator or coil or...."

COIL...??

Put a 3mf ("m" = millifarad) on the CDI coil would kill the CDI instantly.

Guru944 meant to say 3uf..

But that would also compromise the CDI....

[wwest]

Originally Posted by Targalid

Wwest,
Thanks for your knowledge. Maybe you can explain this wikipedia entry to us.

"Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a modulation technique that conforms the width of the pulse, formally the pulse duration, based on modulator signal information. Although this modulation technique can be used to encode information for transmission, its main use is to allow the control of the power supplied to electrical devices, especially to inertial loads such as motors. In addition, PWM is one of the two principal algorithms used in photovoltaic solar battery chargers,[1] the other being MPPT.
The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the load is.
The PWM switching frequency has to be much faster than what would affect the load, which is to say the device that uses the power. Typically switchings have to be done several times a minute in an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies."

So the voltage regulator supplies an exciter voltage to the alternator which is pulsed? This pulsed signal is radio frequency which is picked up by the car radio receiver? Is that the take home message? I'm a chemist not a EE so for me this is like Greek to that guy in Shakespeare.

"...this pulsed signal is radio frequency..."

No. probably something in the range of 50-500Hz.

The PWM cycle...Initially the voltage regulator relay NC contacts are supplying source voltage to the alternator rotor windings, whereupon the alternator output voltage begins to rise. Rate of rise is primarily a function of battery state of charge, 80% battery charge = rapid rise to voltage regulator relay activation voltage. 30% battery charge, slower rise to VR relay activation.

PWM period/rate is primarily a function of battery state of charge.

Older VR's had 2 fairly high wattage resistors (wirewound/nichrome) one in series with the rotor winding to limit the maximum rotor winding current flow, and a second one in parallel with the rotor windings as a "damper" to provide a rapid decay of the rotor magnetic field when the VR relay contacts open.

Absent this "damping" function, and the ~3uF capacitor/condenser, a huge RFI/EMI spike would result from the collapsing rotor winding magnetic field, very much comparable to the Kettering ignition system coil primary.

Basically a mechanically, relay, implemented switching voltage regulator.

[guru944]

Watsondenmark:

Thanx, WWest your are correct, it should be 3 Micro Farad


For CDI Ignition, look into MSD 8830 26Kufd Capacitor.

Noise Capacitor, 26 Kufd - 8830



Later...

[watsondenmark]

Thanks guys. This is way to technical for me - a lot of abbreviations and meassuring values. Sorry guys.

I have the original radio noise thing in it's original place, I just need to know where to put the red wire, and what to plug on to the available base.

I don't expect that it will do anything different about the driving. The car runs fabulous without it.

[wwest]

Originally Posted by guru944

Watsondenmark:

Thanx, WWest your are correct, it should be 3 Micro Farad

But should only be used if one still has the original Kettering ignition system, points, condenser, etc....



For CDI Ignition, look into MSD 8830 26Kufd Capacitor.

But might not a capacitor of this size, MAGNETUDE, sink enough current to adversely affect the alternator PWM dutycycle?

Sort of like putting a small motorcycle battery in the engine compartment which would then get priority in charging over the main battery.

Noise Capacitor, 26 Kufd - 8830



Later...

And what about the HEAT in the engine compartment..with an electrolytic capacitor of this capacity?

I think I would use an LC filter before resorting to this.

[bullmtl]

The pdf-pn8830 instructions-show cap. to be polarized (+ -) connected appropriately
across main feed (red black) wires of MSD UNIT.
Don't believe that LARGE cap. was meant for this low power app.